1. Field of the Invention (Technical Field)
The invention relates to a multichannel sound system comprising multiple microphones and multiple loudspeakers, and a method for its use.
2. Description of the Related Art Including Information Disclosed under 37 C.F.R. .sctn..sctn.1.97-1.99 (Background Art)
A sound system comprising multiple microphones and multiple speakers typically finds use in conference rooms, meeting rooms council chambers, and the like. Normally, such confined acoustic spaces result in microphones being in close proximity to loudspeakers. This proximity either requires an unacceptably low sound system gain, or results in unwanted audio feedback if gain is increased. Accordingly, it is desirable to automatically and gradually attenuate loudspeakers near active microphones to limit unwanted audio feedback. Automatic rate controlled loudspeaker attenuation is also desirable to provide more natural and pleasing sound reinforcement to those seated near the active microphones.
U.S. Pat. No. 3,508,007, to Goodall, et al., entitled Conference Switch for a Multiple Channel Digital Telephone System, discloses a conference sound system wherein only a single digital signal source having a predetermined amplitude is communicated. Other signal sources are totally inhibited, not attenuated.
U.S. Pat. No. 3,992,584, to Dugan, entitled Automatic Microphone Mixer, discloses a sound system wherein input signals in each channel are attenuated by the ratio that the input signal in that channel bears to the sum of all input signals in all channels. Attenuation is without regard for proximity of the input signal source to loudspeakers.
U.S. Pat. No. 4,068,092, to Ikoma, et al., entitled Voice Control Circuit, discloses a sound system wherein voice signals are attenuated according to constant amplitude noise content. No consideration is accorded microphone and loudspeaker proximity.
U.S. Pat. No. 4,184,048, to Alcaide, entitled System of Audioconference by Telephone Link Up, discloses a system wherein priority is accorded the first active signal source, regardless of amplitude, while inhibiting remaining signal sources. Signal sources are symmetrically arranged about a loudspeaker; only signal components resulting from acoustical coupling between loudspeaker and opposing signal sources are canceled.
U.S. Pat. No. 4,449,238, to Lee, et al., entitled Voice-Actuated Switching System, teaches a computer based sound system wherein a microphone with the greatest output level is "selected" while all others are either attenuated or off. No consideration is accorded proximity of microphone and loudspeakers.
Perhaps most relevant is U.S. Pat. No. 4,598,418, to Griffith, Jr., et al., entitled Sound System Employing Automatic Proportional Amplification. Although three fixed attenuation levels for each speaker are disclosed, they are not necessarily optimum for any given application. Further, switching between attenuation levels is virtually instantaneous, resulting in undesirable "clicking" in the system. Lastly, this system can be programmed only by pre-selection of circuit component parameters and "hardwiring;" field programming is rendered cumbersome and difficult.
Lacking in the prior art is a sound system wherein specific speakers may be variably and gradually attenuated depending upon speaker location. The prior art further fails to disclose sound systems that prevent unwanted audio feedback by rate controlled attenuation of selected speakers.